The present invention generally relates to lockbolts, and more specifically relates to a multi-lobular lockbolt which is configured to be installed vis-a-vis a collar which is swaged onto the bolt.
Some conventional lockbolts include a frangible pintail while others do not. As shown in FIG. 1, a typical lockbolt 10 which includes a frangible pintail 12 includes: a head 14, a threaded shaft 16 and a frangible pintail 12 having annular ribs 18, wherein the head 14 is at one end 20 of the bolt 10, the frangible pintail 12 is at the other end 22 of the bolt 10, and the threaded shaft portion 16 is disposed between the head 14 and the frangible pintail 12. As shown in FIG. 1, initially the frangible pintail 12 and threaded shaft 16 is inserted through apertures 24, 26 provided in two or more work pieces 28, 30, and a collar 32 is slid onto the bolt 10, positioned proximate the threaded shaft 16. Then, as shown in FIG. 2, an installation tool 40 is engaged with the collar 32 and the frangible pintail 12. Specifically, as shown in FIG. 3, jaws 41 of the installation tool 40 grip and pull on the pintail 12 (as represented by arrow 42) while an anvil 43 of the installation tool 40 pushes down on the collar 32 (as represented by arrows 44), causing the collar 32 to swage down onto the bolt 10. The swaging causes the collar 32 to deform and generally grip onto the threaded shaft portion 16 of the bolt 10. Once the collar 32 has been swaged, the pintail 12 continues to be pulled until it breaks off, as shown in FIG. 4, leaving the bolt 10 installed in the work pieces 28, 30, secured by the collar 32. Similarly, if the lockbolt is provided as being of the type which does not include a frangible pintail, the threaded portion of the bolt is gripped and pulled as the collar is swaged, and once the collar has been fully swaged, the bolt is released leaving the threads undamaged.
Such lockbolts and tools for installing such lockbolts are generally known in the art. For example, a typical tool for installing lockbolts with frangible pintails is disclosed in U.S. Pat. No. 2,114,493, and includes an anvil for swaging the collar and jaws for gripping and pulling on the pintail.
The threads of some prior art lockbolts, such as that which is shown in FIGS. 1-4, are helical. Regardless of whether the lockbolt includes a frangible pintail or not, the helical threads provide that once the lockbolt has been installed (i.e., the collar has been swaged onto the bolt), the collar can be rotated off of the lockbolt, and thereafter can be threaded back on to the lockbolt (or a new nut threaded onto the lockbolt). A problem associated with providing a lockbolt having standard helical threads is that the collar, once swaged onto the lockbolt, is susceptible to vibrating loose.
U.S. Pat. No. 2,531,048 discloses a lockbolt which tends to solve this problem. The lockbolt, instead of including standard helical threads, includes annular ribs. Being annular rather than helical provides that once a collar is swaged onto the ribs, the collar is not susceptible to vibrating loose. However, the lockbolt presents a new disadvantage: once a collar is swaged onto the ribs, the collar must be broken off of the ribs, rather than be rotated off the ribs. As such, the collar cannot be removed and rotated back onto the lockbolt. In fact, due to the ribs being annular, even a new collar cannot be threaded onto the lockbolt. Instead, the swaging process must be repeated to re-secure the lockbolt.